1. Field of the Invention
The present invention relates to a monostable multivibrating circuit which is also referred to as a one-shot pulse generating circuit. More particularly, it relates to a monostable multivibrating circuit in which the number of circuit elements can be determined regardless of a length of duration of the one-shot pulse.
One-shot pulses are generally pulses each having a relatively short duration and employed in various uses, for example, as a reset signal or a timing signal in semiconductor memory devices. To this end, a one-shot pulse generating circuit (i.e., monostable multivibrating circuit) is incorporated into various semiconductor devices and thus widely utilized.
2. Description of the Related Art
In a known example of the monostable multivibrating circuit, a plurality of gate circuits each having a predetermined operation delay time are employed in combination to generate a one-shot pulse. In this case, the duration of the one-shot pulse is determined by the respective operation delay times in each gate circuit or the differences therebetween. In other words, the number of gate circuits to be required is determined in accordance with the duration of the one-shot pulse. This results in a problem in that, where a one-shot pulse having a relatively long duration is generated, the number of stages of gate circuits to be used is accordingly increased.
Also, due to the increase in the number of the gate circuits, a problem occurs in that an occupation area of the circuits in a semiconductor device is relatively increased and a power dissipation thereby also becomes increased. Furthermore, where a plurality of one-shot pulses each having a duration different from each other are generated, the corresponding plurality of monostable multivibrating circuits must be prepared. In this case, the respective circuit constitutions are different from each other. As a result, a drawback occurs in that it is difficult to standardize a circuit designing of a semiconductor device provided with one-shot pulse generating circuits
Another example of the monostable multivibrating circuit is known in Japanese unexamined Patant Publication No. 2-134912. The circuit constitution includes an exclusive-OR circuit constituted in the form of an emitter-coupled logic (ECL), which includes two pairs of transistors each pair having emitters commonly connected to each other and receiving an identical input signal and an identical reference voltage, and one pair of transistors each having an emitter commonly connected to each other and receiving another input signal and another reference voltage. According to the circuit constitution, a one-shot pulse is output when the two input signals are at an inverse logic level to each other. There is posed, however, a problem in that the constitution of the ECL circuit relatively becomes complicated.
Note, the problems in the prior art will be explained later in detail in contrast with the preferred embodiments of the present invention.